Tunable high-frequency circuit



Feb. 27, 1951 A. E. ABBOT ET AL TUNABLE HIGH-FREQUENCY cmcun Filed Jan. 26, 1946 III/r!!! 4pm 5 H 00 o N v r 6 4 A TTORNEY Patented Feb. 27, 1951 T 2,542,974 TUNABLE HIGH-FREQUENCY CIRCUIT Abraham E. Abbot, New York, and Harry W.

Dryden, Malverne, N. Y., assignors to Federal Telephone and Radio Corporation, New York,

UNITE STATES PATENT OFFICE.

N. Y., a corporation of Delaware Application January 26, 1946, Serial No. 643,784

. 3 Claims. I

The present invention relates to tunable high frequency circuits and particularly to tunable high frequency electron discharge device arrangements of the coaxial line type.

In tuning high frequency circuits of the transmission line type (usually in the ultra high frequency range), a shorting device is used to connect the two conductors formin the transmission line, and is moved back and forth along both conductors to determine the tuning. This type of tuning, while often allowing tuning over a relatively wide range, introduces contact resistances at the points where contact is made by the shorting device with its associated conductors. This lowers the Q of the circuit affected and in troduces other undesirable efiects, particularly where fairly large amounts of energy such as for example, kilowatt or over, are involved. Furthermore, movement of the shorting device from a pre-set position due to vibration or accidental contact, etc, may cause detuning of the system. In addition, it has long been known that line tuning adjustments are diiiicult, if not impossible to make, where sliding, shorting devices are employed.

An object of the present invention is the provision of an improved tunable high frequency circuit.

Another object of the present invention is the provision of improved tuning means for a high frequency circuit of the coaxial line type.

Another object of the present invention is the provision of an improved high frequency circuit which may be tunedover a relatively wide range and which enables the making of relatively fine tuning adjustments.

A further object of the present invention is the provision of an improved coaxial line electron discharge device arrangement including improved tuning means.

A still further object of the present invention is the provision of an improved coaxial line amplifier.

Still another object of the present invention is the provision of an improved coaxial line electron discharge device arrangement in which the electron discharge device is provided with cooling means as well as with tuning means.

While the invention itself is defined in the appended claims, the invention, together with other and further objects and features thereof, will be best understood from the following description of an embodiment thereof, reference being had to the drawing, in which the figure is a schematic elevational view, partially broken away, of a coaxial line electron discharge device arrangement embodying our invention.

Referring generally to the arrangement illustrated in the drawing, an electron discharge device of the type in which the grid serves as an electrostatic shield between the anode and its leads and the cathode and its leads, is arranged within a coaxial line structure, with the grid coupled to the outer or ground conductor through a capacity. The arrangement also includes an adjustable grid bell which is used to control the stability of the amplifier, as is more fully described in the copending application of G. J. Lehmann-B. M. Charchian, Serial No. 588,970, filed April 17, 1945, now Patent No. 2,436,934, issued March 2, 1948. The arrangement includes a plate circuit of the coaxial line type, that is, a circuit between the grid and plate, and also includes a cathode circuit between the grid and cathode. In addition, in the cathode circuit, the grid bell extends between the cathode condoctor and the outer conductor. Tuning is accomplished in the plate circuit by means of a slidable short-circuiting device and a micrometer-adjusted capacity toward the high potential end of the plate or anode circuit. The cathode circuit is tuned by a sliding, shorting device, which may be of conventional design, and the length of the grid bell is adjustable to allow proper adjustment for the desired gain and stability. The anode is cooled by a liquid, which may be water, although it will be appreciated that other fluid means such as for example, aircooling may be employed in place thereof.

Referring now more specifically to the drawing, the arrangement there illustrated includes an electron discharge device or triode I of the type in which the grid serves as an electrostatic shield between the anode and its leads and the cathode and its leads. Means are provided associated with the anode, cathode and grid to form an anode transmission line circuit 2, and a cathode transmission line circuit 3, with the grid ring 4, which serves as the external terminal for the grid, being capacitively coupled to an outer conductor or conductors, generally designated by the numeral 5, which conductor or conductors 5 form the outer conductors of both transmis sion line circuits 2 and 3. For this purpose, the grid ring 4 is supported on, and makes electrical contact with, a metallic member 6 which is annular in configuration and which rests upon an annular sheet of insulating material, such as a mica ring 1, which latter, in turn, rests on another conductive annular member 8., The memher 8 is surrounded by, and electrically in contact with, a cylindrical conductor 9 which forms the outer conductor of the cathode transmission line circuit. Another cylindrical member It] is in electrical contact with the member 8, the cylindrical member In forming the outer conductor of the anode transmission line circuit.

Since the arrangement herein described is adapted to handle about a kilowatt of power and more, means are provided for cooling the anode II. For this purpose the anode is formed with an internal opening within which is provided cooling vanes 12. An adapter I3 is brazed or otherwise secured to the anode II, the adapter l3 having an external thread l4, on which is screwed an internally-threaded coupler !5, the coupler l having an inlet pipe I6 and outlet pipes I1 (three of which are visible in the drawing) secured thereto and extending therein. The inlet pipe le extends through a coupling 18 while the outlet pipes ll extend into said coupling 18 in which the liquid from said outlet pipes is mingled and fed to a single outlet pipe E9.

The inner conductor of the anode transmission line circuit 2, generally designated by the numeral 23, includes the outer surfaces of the anode H, the adapter i3, the coupler i5 and a cylindrical bellows 21, the upper end of which is fastened, as by welding, to the bottom of coupler I5, all of said surfaces being of highly conductive material.

To tune the anode transmission line or anode circuit, a shorting member in the form of an annular transversely-extending disk 22 is provided for rough tuning. The inner end of shorting disk 22 is connected to the bottom of the cylindrical bellows 2!, the perimeter of disk 22 making contact with the inner surface of cylindrical member it) which latter forms the outer conductor of the anode transmission line circuit 2.- When disk 22 is moved upwardly, the length of the anode circuit is shortened and when it is moved downwardly, the length of the anode circuit is lengthened.

To adjust the position of disk 22, a cylindrical member 23 extends from the bottom of disk 22 pins 21 entering the annular slot 25 in flange 24- and moving freel within said slot. As ring 26 is rotated, the pins 2? ride upwar ly or downwardly in their spiral slot, depending upon the direction of rotation of ring 26 and the inner ends of said pins move in the slot 25 in flanges 24, causing the flange to move upwardly or downwardly and thereby moving shorting disk 22.

In order to provide for an excellent contact between the perimeter of disk 22 and the outer conductor it], and to lock the disk 22 rigidly in position after it has been adjusted, a plurality of longitudinal slits 29 are cut in the outer conductor it. These slits 29 make the wall of the outer conductor flexible at the point where said slits are made. Consequently, by arranging a clamp 30 around said outer conductor It over said slits 29 and by tightening said clamp 33, the wall of the outer conductor It at this point is '4 bent inwardly and presses against the perimeter of shorting disk 22 to thereby provide an excellent contact therewith.

For fine tuning, a variable capacitive means is arranged adjacent the high potential end of the anode circuit 2. However, due to the presence of glass 3| surrounding the upper end of the anode, which glass is liable to fracture if the glass itself 'is used as part of the dielectric between the anode and the other member formingthe variable capacity, the variable capacity is formed a distance below the glass. The variable capacity tuning means may consist of a metallic disk or plate 32 arranged at one end of a micrometer 33 and adapted to be'moved in finely graduated adjustment toward or away from the inner anode conductor 20, byadjustment of the micrometer knob 34. The micrometer 33 extends through, is supported by, and makes electrical contact with conductor It.

The cathode transmission line circuit has cylindrical conductor 9 as its outer conductor and the cathode inner conductor may also be a cylindrical member 35 which carries the high frequency current but is preferably insulated from the D. C. voltages. The cathode transmission line circuit may be tuned by any suitable device which shorts at radio frequency the cathode conductor 35 to its outer conductor 9. This may be a capacitive short, or a galvanic short where the direct current applied to the cathode is kept away from the cathode conductor 35 and the cathode conductor 35 only carries the radio frequency. The shorting device is, of course, made adjustable in any manner well-known in the art for pur poses of tuning.

To control the stability of the amplifier arrangement illustrated in the figure, use is made of a grid bell 36 which consists of a fixed cylindrical member 31, resting on and making electrical contact with the metallic annular member 6 connected with the grid ring 4. Thus member 31 is electrically, connected to grid ring 4. The grid bell 36 further includes another cylindrical member 38, surrounding member 31 and making frictional contact therewith, but the oute'r cylindrical member 38 is adapted to be moved .in relation to fixed cylindrical member 31 so as to vary the effective length of the grid bell.

For varying the length of the grid bell, the inner cylindrical member 31 is provided with a plurality of spiral slots 39 within which. project screws or pins 40 fastened in the outer cylinder 38. At the top of outer cylindrical member 38 is provided an annular member 4| similar to annular flange 24 and provided with an annular slot 42 facing outwardly. One or more longitudinal slots 43 are provided in the outer conductor 9 through which project or may be inserted rods 44, preferably made of a suitable insulating material such as for example, polystyrene and which enter the annular slots 42. By raisin or lowering the rods 44 by suitable mechanism or by hand, the annular member 4| is raised and rotates because of the movement of pins 43 in the drawing includes the use of a clamping ring 45 for clamping the grid ring 44 in position on metallic ring 6. In one embodiment, the micrometer 33 was made of steel and it was covered with a brass skirt 46 to prevent overheating of the steel in the high frequency fields. A gasket 41 of rubber may be employed in making a watertight connection between the coupler l5 and the adapter l3.

The radio frequency output from the arrangement may be taken off by a coaxial line 48 whose inner conductor 49 may be arranged to make contact with the anode inner conductor 20.

The outer conductor I and the anode ll may be at ground potential D. C., and for this purpose a source of D. C. potential 50 may have its positive side connected to ground and through the conductors of coaxial line 2 to the anode. negative side of saidsource 50 is connected to the cathode as indicated by line 5|, but this D. C. potential is kept off the cathode line 35. Thus in adjusting or handling the arrangement described, the danger of contact with a high potential is avoided. Furthermore it becomes possible to connect the cooling pipes directly to the anode Without the necessity for insulating the anode from the cooling conduits.

The length of the bell in one embodiment of the present invention was adjusted to about .80 of a wavelength for good gain and maximum stability while the anode circuit was effectively a quarter wavelength. When the aforementioned arrangement was operated at 485 megacycles, it was found to be tunable by means of moving the disk 22 through approximately megacycles, and tunable with the variable condenser arrangement by adjustment of the micrometer knob 34 through 35 megacycles,

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of our invention.

We claim:

1. A coaxial line type resonator for coupling between the anode and grid of a coaxial line type electron discharge device comprising a hollow inner conductor including a conductive member adapted for securing to an anode of an electron discharge device and having conduits for circulating cooling fluid about the anode and metallic bellows having one end thereof attached to said member and the other end extending axially away The from said member, an outer conductor for with said conductive member and said bela coaxial line type resonator, said outer conductor having a transversely flexible portion thereof, means for tuning said coaxial resonator including an annular shorting disc having its inner edge secured to and in electrical contact with said bellows and its outer edge in contact with the inner wall of said outer conductor adjacent said transversely flexible portion, and means for pressing said portion of said outer conductor against the outer edge of said shorting device.

2. A coaxial line type resonator according to claim 1, further including a micrometer extending through the outer conductor and electrically connected therewith, a plate secured to the inner end of said micrometer and adapted to be moved toward or away from the anode inner conductor for tuning the anode circuit.

3. A resonator according to claim 1 in which said outer conductor is provided with a spiral slot and a pin is connected to said shorting disc and extended through said spiral slot for moving said shorting disc and additionally locking it in position.

ABRAHAM E. ABBOT. HARRY W. DRYDEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,145,022 Keufiel July 6, 1915 2,086,615 Grundmann July 13, 1937 2,159,782 Conklin et a1 May 23, 1939 2,169,305 Tunick Aug. 15, 1939 2,226,479 Pupp Dec. 24, 1940 2,249,443 Tringham July 15, 1941 2,358,462 Mahren Sept. 19, 1944 2,353,742 McArthur July 18, 1944 2,395,851 Cork Mar. 5, 1946 2,411,424 Gurewitsch Nov. 19, 1946 2,408,355 Turner Sept. 24, 1946 2,425,352 Sloss Aug. 12, 1947 2,434,115 McArthur Jan. 6, 1948 2,446,405 Bels Aug. 3, 1948 

